a) Field of the Invention
The present invention relates to an anchor device for terminals of optical fibers of an optical cable which uses a loose tube type unit or has a similar configuration and more specifically an anchor device preferably used for a submarine cable to which high tension is applied from outside.
b) Description of the Prior Art
There is a trend to use, instead of a tight type optical fiber unit which has been conventionally used as an optical fiber unit to be disposed in a center of a submarine cable, a loose tube type unit which has been developed for passing a larger number of optical fibers to meet a demand for a larger number of communication circuits.
Referring to FIG. 1A, FIG. 1B and FIG. 1C, description will be made of a difference between the tight type unit and the loose tube type unit.
As shown in FIG. 1A as a schematic sectional view, a tight type fiber unit 80 has a configuration in which a center high tensile strength body 80b such as a steel wire is disposed at a center of an optical fiber unit, several optical fibers 1a are filled and held around the center body 80b by way of urethane acrylate-based resin 80c, and an outer circumference is formed as a cover layer made of urethane acrylate-based resin which is hard at a certain degree.
A loose type unit 1 which is shown in FIG. 1B has a configuration in which a plurality of optical fibers 1a are inserted into a loose tube 1d made of extruded resin such as polybutylene terephthalate (PBT), polypropylene (PP) by way of a jelly like filler (compound) 1c. 
In addition, the optical fibers 1a can be supplied also in a form of an optical fiber tape le which preliminarily restricts several optical fibers in a form of a tape as shown in an enlarged view E in FIG. 1C.
Then, description will be made of a configurational example of a submarine optical cable which uses the loose tube type unit referring to a perspective view shown in FIG. 2 and a sectional view taken perpendicularly to an axis of the cable shown in FIG. 3. In these drawings, a reference numeral 1 represents a loose tube type optical fiber unit and a reference numeral 2 designates a pressure-resisting layer for protecting the loose tube type unit 1 from a water pressure which consists of three divided pieces 2a having a sectorial section and made of a metal such as iron in FIG. 3.
A compound 7 having stickiness and glueability is filled between a loose tube 1d and an inside surface of the pressure-resisting layer 2 so that the loose tube 1d is restricted by way of the compound 7. A tensile strength body layer 3 which is composed by intertwisting a plurality of steel wires 3a is disposed around an outer circumference of the pressure-resisting layer 2 so as to sufficiently cope with a tensile force to be applied to the cable and the tensile strength body layer 3 is formed as a single layer in this example. A compound 8 is filled intermittently in a longitudinal direction in a space partitioned by an outer circumferential surface of the pressure-resisting layer 2, an inner circumferential surface of a metal tube layer 4 and an outer circumferential surface of a tensile strength wire 3.
The tensile strength layer 3 which is formed as the single layer in FIG. 2 is composed by intertwisting mainly steel wires so that the layer 3 can cope sufficiently with the tensile force to be applied to the cable.
The tensile strength body layer 3 consists of a single layer or a plurality of layers, affords tensile strength sufficiently bearable of a load to be applied at a cable laying stage and protects the cable from hindrance.
A reference numeral 4 represents a metal tube layer which maintains unity and airtightness of the above described tensile strength body layer 3, functions as a power feeder to a repeater and is formed as a tube usually by welding a metal tape made of copper, alminium or the like along the tensile strength layer so as to reduce a diameter.
Furthermore, reference numerals 5 and 6 denote insulating layers (sheaths) made of polyethylene or the like which are formed for insulation from sea water and mechanical protection.
A cable which has a configuration different from the above described configuration is also used as a tensile strength body layer. In an example shown as a perspective view and a sectional view shown in FIG. 4 and FIG. 5, a configuration of a pressure-resisting layer is changed. Speaking concretely, a pressure-resisting layer is composed so as to realize a pressure resisting shell around the outer circumference of the loose tube type unit 1 by competition between tensile strength wires which are intertwisted into two layers of an inner layer consisting of tensile strength wires 3a and an outer layer consisting of tensile strength wires 3b. 
The compound 7 having the stickiness and glueability is filled between the outer circumferential surface of the loose tube type unit 1 and a curved surface on a side where the tensile strength wires 3a are opposed to the loose tube type unit 1 so that the pressure-resisting shell (substantially a shell having a diameter determined by inside surfaces of the tensile strength wires 3a) restricts the loose tube 1d. 
The metal tube layer 4, and the insulating layers 5 and 6 which are disposed around the metal tube layer 4 are composed as those shown in FIG. 2 and FIG. 3.
Since such a submarine optical cable is usually laid between a continent and a continent or between a continent and an island, long cables are laid on a sea bottom by way of repeaters for relaying transmitted signals. Since it is necessary to connect the long cables to the repeaters and the long cables at a plurality of locations, optical, electrical and mechanical connection (the so-called anchoring) is required for this kind of submarine optical cables by connecting the optical fibers 1a and the metal tube layers 4 to one another and firmly fixing the so-called tensile strength bodies such as the divided pieces composing the above described pressure-resisting layer 2 and the tensile strength wires 3a and 3b composing the tensile strength body layer 3 so that the submarine cables can be laid under a deep sea and recovered from the deep sea.
As an anchor device for the loose tube type optical fibers, there is known an optical fiber anchor device which is configured to anchor optical fibers by forming an optical fiber anchor location of a bonding agent in a form of a tape, inserting these optical fibers in the form of the tape into a run-through hole of a shrinkable tube, integrating the fibers with the tube by heating, accommodating the shrinkable tube into a fixing member and fixing the fixing member (for example an optical fiber anchor device disclosed by Japanese Patent Kokai Publication No. 2001-108840).
The optical fiber anchor device disclosed by this publication is configured to anchor optical fibers by a lateral pressure of a shrinkable tube and a frictional force of a bonding agent.
Submarine optical cables are connected by way of terminal connecting devices. In the terminal connecting devices, connected portions of optical fibers are accommodated in pressure-resisting cylinders so that the cables function under a high pressure on a sea bottom. Since the pressure resisting cylinders have strength sufficiently bearable not only of a high pressure of sea water but also of tensile forces from cables on both sides, tensile forces of the submarine optical cables are transmitted to each other by way of the pressure-resisting cylinders in the terminal connecting devices.
In order to connect the submarine optical cables to these terminal connecting devices, the submarine optical cables are therefore anchored by fixing terminals such as the divided pieces 2a and the tensile strength wires 3a to the pressure resisting cylinders or members which are fixed to the pressure-resisting cylinders.
Since it is supposed that a maximum tension to be applied to each submarine cable is on the order of breaking loads of component members of the cable, it is desirable to anchor all the component members. Furthermore, a case is apt to occur where the component members are pulled into the cable by tension, it is necessary to firmly anchor the optical fiber itself to a fixed portion of the terminal connecting device.
Japanese patent Application No. 2002-63172 applied by the inventor proposed a method for anchoring an internal jelly-like filler and optical fibers simultaneously via a loose tube by twisting the loose tube around a drum-like anchor disk shown in FIG. 6A and a method for independently anchoring optical fibers in a loose tube using a bonding agent as shown in FIG. 6B.
FIG. 6A is a sectional view of a portion of a joint box (JB) 20 which is a kind of terminal connecting device taken along a plane including an axis line of a submarine optical cable.
A surface of a pressure-resisting cylinder 28 which is a main body of the JB 20 is covered with an insulating material 27. The pressure-resisting cylinder 28 is a cylinder made of a metal having high strength, and an anchor disk 11 is inserted into holes at centers of flat panels formed at both ends of the cylinder and held by the pressure-resisting cylinder 28 at color portions of the anchor disk 11.
A submarine optical cable 50 is inserted from a right side into a hole at a center of the insulating material 27. The submarine optical cable 50 is, for example, of a type which has the loose tube type unit shown in FIG. 2.
A metal tape layer 4 and insulating layers 5 and 6 are removed from the cable 50, divided pieces 2a composing a pressure-resisting layer 2 and a tensile strength wires 3a composing a tensile strength body layer 3 are disposed in a tapered hole at a center of the anchor disk 11 in spread conditions and clamped by pressing in a tapered pin 13. For positioning, the tapered pin 13 is pressed with a clamp nut 15 by way of a flange 14.
A tensile force applied to the cable 50 is transmitted from the divided pieces 2a and the tensile strength wires 3a to the pressure-resisting cylinder 28 by way of the anchor disk 11 and the tapered pin 13, and further to a cable (not shown) connected to a left end.
A reference numeral 60 used in FIG. 6A represents an optical fiber anchor device which anchors a loose tube and optical fibers at the same time. A loose tube type unit 1 of the cable 50 is passed through the tapered pin 13, the flange 14 and a run-through hole of the clamp nut 15, is guided by a wrapping guide 16 and attains to an interior of the pressure-resisting cylinder 28. In the pressure-resisting cylinder, a nearly cylindrical winding disk 61 is fixed to a base plate 62 fixed to the pressure-resisting cylinder 28, and the loose tube type unit 1 is wound several turns around a cylindrical outer circumferential surface of the winding disk 61 and an end of the lose tube type unit 1 is fixed to the base plate 62 with a terminal fixing implement 63.
A force exerted from the terminal fixing implement 63 to the loose tube type unit 1 is expanded by a frictional force of a twisted portion of the loose tube type unit 1 wound around the outer circumference of the winding disk and anchors the loose tube type unit 1, and the internal optical fibers 1a are also anchored by frictional force of the charged jelly-like filler 1c. 
On the other hand, an optical fiber anchor device 70 shown in FIG. 6B is an anchor device using a bonding agent and disposed at a location which is substantially the same as a location of an optical fiber anchor device 60 shown in FIG. 11A. Divided pieces 2a and tensile strength wires 3a are anchored similarly to those shown in FIG. 6A and a loose tube type unit 1 is led linearly into a pressure-resisting cylinder 28.
A loose tube 1d of the loose tube type unit 1 is anchored to a loose tube bonding implement 72 with a bonding agent or the like.
Then, the loose tube 1d is removed from the loose tube type unit 1, optical fibers 1a are taken out, a jelly-like filler 1c is wiped off, and the optical fibers 1a are arranged in grooves in a bonding implement 73 and bonded to the grooves with a bonding agent. Used as the bonding agent is epoxy resin or UV curable type resin.
In order to reduce a number of component members of a submarine optical cable, it is proposed to configure an inner circumferential surface of a pressure-resisting shell to have a function of a loose tube.
For example, FIG. 7 is a perspective view showing two kinds of configurations of submarine optical cables which use no loose tube but have optical fiber accommodating structures in functions equivalent to that of the loose tube type unit.
In a first configuration shown in FIG. 7, a cylindrical pressure-resisting layer 2 is composed by combining divided pieces 2a having sectorial sections, a compound 7 is applied densely to a gap formed by the divided pieces 2a, optical fibers are inserted into an internal space in the divided pieces 2a and a jelly-like filler 1c is filled densely in the gap. A loose tube for composing the loose tube type unit is replaced with the pressure-resisting layer 2 and the compound 7, whereby the loose tube itself is not present.
An example shown in FIG. 7 uses no loose tube, but has a space corresponding to an inner circumferential surface of a loose tube, allows optical fibers 1a and the jelly-like filler 1c to be passed and filled into the space and has a function to hold the optical fibers 1a which is the same as that of the loose tube type unit.
Since a terminal connecting device used to connect a submarine cable must be compact taking its mechanical and handling characteristics, etc. into consideration, compactness is required also for an anchor device for tensile strength body of the cable. A cable anchor device must also be compact since optical cables must be handled so as not to apply unreasonable mechanical tension to connected optical fibers and a excess length accommodating body for accommodating excess lengths of optical fibers and the like are disposed in a pressure-resisting cylinder.
A diameter of the winding disk used in the conventional example is restricted by an allowable radius of curvature which does not degrade a transmission characteristic of the optical fibers. Also in a case where the optical fibers are to be bonded linearly with a bonding agent, the optical fibers must be bonded for a pretty long distance for anchoring the optical fibers securely. Furthermore, the winding disk and the optical fiber bonding implement which are to be accommodated in the pressure-resisting cylinder tend to involve the problem of enlarging the pressure-resisting cylinder.
Furthermore, when it is expected to bond the optical fibers completely with an ordinary bonding agent, a curing time of 8 hours or longer will be required.
Any of the conventional methods involves problems to prolong a working time, enhance a price of equipment, require materials at high cost prices and the like all of which result in enhancement of a manufacturing cost.
Furthermore, it is evident that an optical fiber anchor device which has a configuration similar to that shown in FIG. 6A which anchors optical fibers indirectly with a loose tube is not applicable to a submarine optical cable which is configured to exhibit an effect of a loose tube type unit without using a loose tube.
Furthermore, in a case where optical fibers are anchored by bonding portions of optical fibers into a form of a tape with a bonding agent, inserting the optical fibers in the form of a tape into a run-through hole of a shrinkable tube, integrating the optical fibers by heating and accommodating the shrinkable tube into a fixed member, the tube in which the optical fibers are inserted is shrunk at a location supposed to be attached to the fixed member and the location for attachment must be selected so as to avoid excess loosening or tension of the optical fibers, thereby posing problems of making it difficult to select a location of attachment of the shrinkable tube, requiring a long time to cure the bonding agent for bonding the optical fibers into the form of the tape with the bonding agent, allowing a lateral pressure to degrade a transmission characteristic of the optical fibers when the shrinkable tube is fixed by a mechanical method such as holding the optical fibers with the fixed member at a stage to accommodate the shrinkable tube into the fixed member or the like.